Cylinder assembly for hydraulic actuator



March 27, 1956 s, A, HALL 2,739,571

CYLINDER ASSEMBLY FOR HYDRAULIC ACTUATOR Filed D60. 29, 1952 2Sheets-Sheet l March 27, 1956 AI HALL CYLINDER ASSEMBLY FOR HYDRAULICACTUATOR 2 Sheets-Sheet 2 Filed Dec. 29. 1952 @GMW CYLINDER ASSEMBLY FORHYDRAULIC ACTUATOR Stanley A. Hall, Gardena, Calif., assignor toNorthrop Aircraft, Inc., Hawthorne, Calif., a corporation of CaliforniaApplication December 29, 1952, Serial No. 328,328 2 Claims. (Cl. 121 38)This invention relates to hydraulic actuators and more particularly toworking cylinders for actuators in which it is necessary to maintainminimum dimensions for the cylinder and at the same time deliver amaximum power output.

Available space quite frequently limits the size of a hydraulic actuatorcylinder which can be utilized in a given installation; This isparticularly true in airplanes and guided missiles in which theircontrol surfaces are operated by hydraulic actuators. It has beendetermined that a force of approximately 8000 pounds is required, underextreme operating conditions, to move the aileron control surfaces ofcertain large planes traveling at high speeds. To accommodate ahydraulic cylinder, in the space available in a wing section, largeenough to deliver suilicient force to properly actuate the controlsurfaces presents quite a design problem.

It is, therefore, an object of the present invention to provide aneicient and economical hydraulic actuator, having a working cylinder ofminimum dimensions which may be utilized in installations where space iscritical, and at the same time be capable of delivering7 a force equalto that of a conventional actuator, having a working cylinder of greaterdiameter, when operating under the same conditions.

A further object is to provide a hydraulic actuator in which the wallsof the hydraulic cylinder may be made relatively thin without danger offailure, due to the fluid pressure therein, and yet deliver a forceequal to a conventional cylinder having thicker walls and consequentlygreater overall dimensions.

Other objects and advantages of this invention will be apparent from thefollowing description forming a part of this specification, but theinvention is not limited to the embodiment herein described, as variousforms may be adopted within the scope of the appended claims.

The invention may be more fully understood by reference to theaccompanying drawings, wherein:

Figure l is a diagrammatic perspective View of an airplane showing oneembodiment of the present invention in connection with its aileron cablecontrol system.

Figure 2 is an enlarged perspective view of the hydraulic actuator inits installed position as shown .in Figure l.

Figure 3 is a sectional view of the hydraulic actuator shown in Figure 2taken on the line 3 3 thereof.

Figure 4 is a cross sectional view of the hydraulic actu* ator shown inFigure 3 taken on the line 4 4 thereof.

Figure 5 is a cross sectional view of the hydraulic actuator shown inFigure 3 taken on the line 5 5 thereof.

Referring first to Figure l, for a detailed description of the presentinvention, an airplane 1 is shown having ailerons 2. Each aileron ispivotally moved about its hinge line by two cable controlled hydraulicactuators 3, of the type herein disclosed, located near the end portionsof the ailerons. Each actuator is controlled through suitable linkage bycontrol cables 4 which connect with an aileron control quadrant 5.Movements of the control nited States Patent cylinder assembly through2,739,571 Patented Mar. 27, 1956 by means of a control element 6connected with the quadrant through conventional linkage. Also locatedin the trailing edge of each wing, midway between the aileron actuators3, is a centering spring 7 which is connected with the control cablesthrough suitable linkage. The centering spring provides synthetic feelwhich is fed back to the pilots controls, thereby simulatingconventional control pressures.

One embodiment of the present invention, shown in its installed position(Figure 2) to operate ailerons 2, comprises a valve assembly 8 and acylinder assembly 9. The cylinder assembly at its closed end is attachedto aileron hinge bracket 10 by means of a connector element 11 and hingepin 12, aileron hinge bracket 10 being rigidly attached to a forwardaileron spar 13. A lower hinge pin 14 pivotally secures aileron hingebracket 10 to a wing bracket 15 attached to a lower ange of a rear wingspar 16. The other end of the cylinder assembly'is attached to a thrustbracket 17 by means of its piston rod assembly and pin 19, the thrustbracket being rigidly secured to a stationary structural element of theplane.

Valve assembly 8, as best seen in Figure 3, comprises a spool housing20, a spool casing 21, adapted to be secured in cylindrical bore 22 ofthe housing, and a Valve spool 23. Spool 23 is provided with an integralend p0rtion 24, provided with an eye, bymeans of which the spool isconnected to element 25, which in turn is connected by cables 4 to thepilots control element 6. Movement of spool 23 results in fluid beingadmitted to cylinder assembly 9 to move ailerons 2, the moment arm beingbetween the axis of pin 12 and 14.

Spool housing is provided with fluid inlet and return ports 26 and 27,respectively. The spool casing constitutes a hollow cylindrical sleevexedly secured in housing 20 by means of dowel pin 28 and set screw 29 ina well known manner. The spool casing is provided with fourcircumferential lluid grooves longitudinally spaced on its outersurface. The grooves communicating with inlet and return ports 26 and 27are generally referred to a pressure groove 30 and a return groove 31,respectively, while the other two grooves 32 and 33 are referred to ascylinder grooves as they communicate directly with the various chambersof cylinder assembly 9. As viewed in Figure 3, groove 32 is positionedto the right of pressure groove 30 and supplies uid to chambers C1 andC2 of the passageway 34. Groove 33, positioned between the pressure andreturn grooves, supplies fluid to chambers C3 and C4 through passageways35, 36 and 37, all of these passageways are plugged at their free endsto provide a closed lluid tight path. Separating each of the above iluidgrooves are sealing ring grooves containing sealing rings 38. Sealingring grooves 39 and 40 are also provided at each end of the casing andaround the inner cylindrical surface of the casing, respectively, thegrooves 40 being ad'acent end portions of the casing. Packing, onepreferred form being of the 0 ring type, is positioned in the abovesealing ring grooves to effectively confine lluid to the various tluidpressure grooves and prevent its escape from the end portions of thehousing 20 and casing 21.

Spool 23 constitutes a rod of circular cross-section which is lapped toprovide a near uid tight longitudinal sliding t in bore 41 of casing 21.The longitudinal travel of spool 23 is limited by pin 42 which issecured in the walls of casing 21 and spans the bore 41, passing througha diametrical slot 43 in the spool 23. A longitudinal bore 44 extendsfrom its short of slot 43 in spool 23, open end by a plug 45.

The outer surface of valve spool 23 is also provided with fourlongitudinally spaced circumferential fluid grooves 46, 50, 52 and 53.Groove 46, generally referred quadrant are pilot initiated the borebeing closed at its non-attaching end and terminates" 'to as the spoolpressure groove, is positioned to communicate with pressure groove atall operational positions of the spool, radial passageways 47 providemeans for the .HOW @f ,fluid between .these tvv@ grooves, 1n the spoolsneutral position, Yas Ashown in Figure .3, groove 46 extends an equaldistance on eaeh side of passageway 47 so `that its side walls bisectthe innermost aperture of two groups of rflow holes 48 and 49 ina mannerto be described later. Groove 50, generally kreferred to as the spoolreturn groove, is positioned to communicate withreturn groove 31 at alloperational positions ,of the spool, radial passageways 5 1 providemeans for the ow of liuid between these two grooves. Groove 52,positioned to the right o f spool pressure groove 46 communicates withcylinder groove 32 through ow holes 48 during predetermined positions ofthe spool. Groove 53, positioned between the spool pressure and returngrooves, communicates with cylinder groove 33 also during predeterminedpositions of the spool. Spool grooves 50, 52, and 53 communicate withthe bore 44 of the spool, radial passageways 54 provide means for theflow of iiuid between these respective grooves and the bore. The spoolgrooves 46, 50, 52, and 53 are separated by lands 55, 56, and 57.

The valve assembly construction is completed by the two groups of owholes 48 and 49 referred to above. The deiinite pattern and function ofthe flow holes have been disclosed and claimed in U. S. application No.17,624, dated March 29, 1948, now U. S. Patent No. 2,631,571, issuedMarch 17, 195.3, and constitutes no part of the present inventiontherefore they will not be described in detail in the presentdisclosure. The above ow holes are normal to the peripheral surface ofspool casing 21 and spool 23, all liquid flowing to the cylinderassembly passing therethrough. It should be noted that all fluid flowingto cylinder chambers C1, and C2 must pass through flow holes 48, allreturn fluid from these chambers (C1 and C2) also ows through these sameholes, the same is true of flow holes 49 and chambers C3 and C4.

In a valve as disclosed above, return iluid from any of the cylinderchambers (C1, Cz, C3, or C4) Hows to the boreY 44 located interiorly ofspool 23. Fluid under pressure does not contact either end portion ofthe spool, it is, therefore, not subject to any exterior or unequalfluid pressures which will inherently tend to move the spool from agiven operational position and require additional parts to balance thespool, as in the case in the valve disclosed in U S. Patent No.2,612,872, issued October 7, 1952. Since ther proposed spool isI notcontacted externally by any iiuid it is not subject to movement byhydraulic pressures and is, therefore, inherently balanced as pertainsto non-flow conditions.

Further the balanced condition of the` valve spool permits a materialreduction in the number of parts and consequent machine Work. The valveof the present invention consists of only four major parts while a valveas disclosed in the above referred to application consists of twelvemajor parts.

The cylinder assembly of theA present invention consists of a cylindercasing 58, having a longitudinal cylindrical bore 59, and a piston rodassembly 60. The piston rod assembly includes a cylindrical sleevemember 61 coaxially positionedl with respect to the bore 59,. A rod.connector element 62 is threadably secured tov sleeve member 61, an eye63v in its outer end providing means for securing the actuator toybracket 1,7 in a manner previouslyexplained. At the other end ofcylinder 5,8 an inwardly extending annular shoulder 64 provides abearing surface for one end of sleeve member 61, the other end beingsupported by a removable bearing 65. Positioned between shoulder 64 andbearing 65 is another removable bearing 66, dividing` the bore 594 intotwo chambers. 0f` equal PIO' portions. Bearings 65 and 66 are retainedin fixed relationship with casing 53 by means of pins 67 in a Well knownmanner. The centralbores of bushings 65 and 66 and shoulder 64 provide aslidingY t for: Sleeve member 61, bearings 65 and 66 are provided withconventional sealing grooves 68 and sealing rings 69 rendering thecylinder casing uid tight and precluding the flow of fluid from one sideof bushing 66 to the other.

Pistons 70 and 71 are secured to sleeve member 61 in tixed relationshipto move therewith, the pistons being relatively positioned on each sideof bushing 66 so that they form chambers C1, Cz, Cs, and C4 of equalproportions when the piston rod assembly is in its neutral position. Theouter peripheral surface of each of the pistons 70 and 71 are providedwith a pair of conventional sealing ring grooves and sealing rings. Theperipheral portion of the pistons between their seals are vented to theatmosphere. Venting of the pistons assures instantaneous movement of therod assembly in response to changes of uid pressure in chambers C1 andC2 or Ca and C4, respectively.

To vent the pistons, as outlined above, a circular rod member 72 iscoaxially positioned insleeve member 61 in fluid tight relationtherewith throughout a major portion of its length, a central bore 73extending from piston 71 to its end adjacent shoulder 64. Radialpassageways 81 provide communication between that peripheral portion ofthe pistons between their sealing rings and bore 73. The non-connectingend portion of sleeve element 61 is protected by connector element 11which is threadably secured to the adjacent end portion of cylindercasing 58. Connector element 11 is provided with an eye by means ofwhich it is attached to the aileron hinge bracket as previouslyexplained. An aperture 74, provided in the wall of element 11, completesthe venting system and subjects that peripheral portion of each piston,as mentioned above, to atmosphere pressure or a pressure lower than thatof the iiuid in chambers C1-C4, inclusive.

The cylinder assembly is completed by longitudinal extending grooves 75and 76 provided in the outer peripheral surface of rod 72. Groove 75extends between apertures 77 and 78 in the wall of sleeve 61 therebyproviding a passageway for uid between chambers C3-C4. Groove 76 extendsbetween apertures 79 and 80 providing a passageway for iluid betweenchambers C1 and C2.

With the valve spool in its neutral position, as shown in Figure 3,there. is a relatively small. quantity of uid constantly owing orleaking through the valve assembly. In one preferred embodiment fluidunder a pressure of approximately 3000 p. s. i, enters the valve assembly through port 26. This fluid,during its passage through the valveassembly, Hows through the innermost hole of each iiow hole group as thevertical side walls of groove 46 bisect the innermost hole of each iiowhole group. As the individual holes of each flow hole group are small,and further being bisected by the side walls of groove 46, a pressuredrop of approximately 1500 p. s. i. occurs as liuid ilows therethrough.This pressure is conveyed vto both sides of each piston 70 and 71,creating a preload of approximately l500p. s. i, in cylinder chamber C1,Cs,y C3, and C1, thus preventing motion of any control surfaces undershock conditions, which may be connected to the actuator. Return ilcwoccurs through the outermost hole of each how hole group returning tocentral bore 44 ot the valve spool as is apparent from its position.With. spool 44, in its neutral position, all holes except the innermostand outermost ones of each ow hole group are closed by spool lands 56and 57, respectively.

lf spool 23 is moved to the right of its neutral position more flowholes of group 48 are. opened tothe low of pressure iluid by land 57 andall ow holes of the group are closed to return iluid bythe. same land.Accordingly pressurefluid ows to chamber C1 via groove 32 and passageway3,4. As. cylinder chambers C1 andr C2` are connected by longitudinalypassageway 76 and apertures 79 and 80.: Huid flowing into-chamber C1will also low to chamber C2 causing the, actuator cylinder to move totheright as the pistonsrodfassembly 60|is immovable, the

same being iixedly secured to a structural element of the airplane. Theabove movement of the spool also closes all ilow holes of group 49 @ipressure iiuid but allows luid from chambers C3 and C4 to flow to bore44 and pass from the valve assembly. Under the above conditions,actuator cylinder Sit will continue to move to the right until itreaches a position where the iiuid pressure cting on each side ofpistons 7d and 71 is equal, this pon sition will not be the neutralposition of the valve spool as a portion of the pressure on fluidcontained in chambers C3 and C4 will now be supplied by external forcesacting on the ailerons 2.

From the above, it is seen a fluid pressure cylinder for a hydraulicactuator is provided in which a pair of pistons are mounted in tandem ona common piston rod. The combined iluid pressure area of the twopistons, being equal to a single larger piston, permits a reduction innet cross sectional area of the Working cylinder while maintaining itspower output. Also, as the stress at which the walls of a hydrauliccylinder rupture or burst varies in an inverse ratio to its diameter, areduction in wall thickness is possible. Cylinder walls of lessthickness permit a further reduction in the net cross sectional area ofthe cylinder, accompanied by a saving or reduction in material, weightand space required to mount the subject cylinder,

A comparison of the hydraulic cylinder of the present invention and acylinder of the type disclosed in U. S. application No. 137,622, nowPatent No. 2,619,304, issued November 25, 1952, follows, both operatingat a iiuid pressure of 3000 pounds per square inch.

While in order to comply with the statute, the invention has beendescribed in language more or less specific as to structural features,it is to be understood that the invention is not limited to the speciiicfeatures shown, but that the means and construction herein disclosedcomprises a preferred form of putting the invention into effect, and theinvention is therefore claimed in any of its forms or modificationswithin the legitimate and valid scope of the appended claims.

What is claimed is:

l. In a hydraulic actuator, a casing having a cylindrical bore therein,annular elements positioned in said bore adjacent to the ends thereof, apiston rod arranged coaxially in said bore and extending through saidannular elements in uid tight relationship, annular means surroundingsaid piston rod and dividing said bore into two equal fluid tightportions, a rst piston ixedly secured on said piston rod so that one ofsaid portions is divided into a first chamber adjaceitt one end of saidbore and a second chamber adjacent said annular means, a second pistonlixedly secured on said piston rod so that the other of said portions isdivided into a third chamber adjacent said annular means and a fourthchamber adjacent the other end of said bore, Wall portions of saidcasing defining rst and second passages whereby uid from an externalsource may communicate with said first and second chambers, portions ofsaid piston rod defining a third passage adapted to provide iiuidcommunication between said irst and third chambers, and other portionsof said piston rod defining a fourth passage adapted to provide fluidcommunication between said second and third chambers.

2. In a hydraulic actuator, a casing having a cylindrical bore therein,annular elements positioned in said bore adjacent the ends thereof, apiston rod comprising a cylindrical sleeve arranged coaxially of saidbore and extending through said annular elements in iiuid tightrelationship, annular means surrounding said piston rod and dividingsaid bore into two equal fluid tight portions, a irst piston iixedlysecured to said piston rod so that one of said portionsis divided into aiirst chamber adjacent one end of said bore and a second chamberadjacent said annular means, a second piston xedly secured to saidpiston rod so that the other of said portions is divided into a thirdchamber adjacent said annular means and a fourth chamber adjacent theother end of said bore, wall portions of said casing defining first andsecond passages whereby iiuid from an external source may communicatewith said first and second chambers, wall portion of said piston roddetining a plurality of passages whereby each of said chambers maycommunicate with the interior of said piston rod, a filler rodpositioned within said piston rod in Huid tight relationship andextending substantially throughout the length of said piston rod, outerportions of said filler rod defining a irst groove extending betweensaid radial passages communieating with said rst and third chambers anda second groove extending between said radial passages communieatingwith said second and fourth chambers.

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